1. Field of the Invention
The invention is directed to a hard material head for a rotary percussion drill bit, particularly in the diameter range of 4 mm to 45 mm, especially from 8 mm to 16 mm, and to a rotary percussion drill bit outfitted therewith for use with hand-held rotary percussion power tools.
2. Description of the Prior Art
According to DE10208631, for example, rotary percussion drill bits of the type mentioned above for hand-held rotary percussion power tools are usually outfitted in the end of the shaft with a chisel-type hard metal plate which is brazed at the bottom and along two opposite lateral fastening surfaces into a receiving slot extending diametrically through the shaft end.
DE4419641 discloses a rotary percussion drill bit which is optimized for rotary percussion drilling in reinforced concrete and which has a compact hard material head with main cutters and auxiliary cutters. The hard material head is butt-soldered to the base surface over the bottom area opposite the cutters. When encountering iron reinforcements, the leading auxiliary cutter lifts the drilling head axially somewhat so that it does not hook into the iron reinforcement.
DE4339245 discloses a rotary percussion drill bit which is optimized for rotary percussion drilling in reinforced concrete and which has a square hard material head with main cutters and auxiliary cutters. On the shaft side, the hard material head has a diagonally extending slot for an associated pin of the shaft end that engages therein by positive engagement, i.e., form-locking engagement. Apart from that, the hard material head is butt-soldered.
DE2246965 discloses a butterfly-shaped hard material head with only one diagonally extending cutter and exactly two oppositely located convex and concave side surfaces, respectively. Only the convex side surfaces form circumferential lengthwise peripheral pockets which are open on the shaft side exclusively in the middle portion. Suitably fitting punctiform axial pins of the shaft end associated with the peripheral pockets engage therein by form-locking engagement and form a smooth axial continuation of the side surfaces. Rotary percussion drill bits with only one diagonally extending cutter, that is, exactly two circumferentially distributed cutting edges, tend to jam in iron reinforcements when carrying out rotary percussion drilling in reinforced concrete.
DE10006936 discloses a rotary percussion drill bit with main cutters and auxiliary cutters which is optimized for rotary percussion drilling in reinforced concrete and which has an X-shaped hard material head of sintered material which is soldered in the shaft end exclusively along two oppositely located concave lateral fastening surfaces and the bottom surface into a slot between two circumferential lengthwise axial pins arranged in a suitable X-shape. The associated X-shaped hard material head accord to DE1006936 has a bevel in the bottom surface opposite to the cutting edges exclusively at the oppositely located concave lateral fastening surfaces. The axial pins of the shaft end which project radially over the axial projection of the concave lateral fastening surfaces of the hard material head delimit the removal groove for drillings, which extends to the circumscribing circle, and therefore limits the maximum drilling capacity, especially in the diameter range of 8 mm to 16 mm.